Reappraising the risk and benefits of aggressive glaucoma therapy

An Intraocular Pressure Measurement Technique Based on Acoustic Radiation Force Using an Ultrasound Transducer: A Feasibility Study

High intraocular pressure (IOP) is one of the major risk factors for glaucoma, and thus accurate IOP measurements should be performed to diagnose and treat glaucoma early. In this study, a novel technique for measuring the IOP based on acoustic radiation force was proposed, and its potential was experimentally demonstrated. The proposed technique uses the acoustic radiation force to generate axial displacement on the ocular surface while simultaneously measuring the degree of deformation. In order to verify that the ocular displacement induced by the acoustic radiation force is related to the IOP, the experiment was conducted by fabricating a 5 MHz single element transducer and gelatin phantoms with different stiffness values. Our experimental results show that there is a close relationship between the ocular displacement by the acoustic radiation force and the IOP obtained by a commercial tonometer. Therefore, the proposed acoustic radiation force technique can be a promising candidate for measuring the IOP.

The critical role of the conjunctiva in glaucoma filtration surgery

This review considers the critical role of the conjunctiva in determining the success or failure of glaucoma filtration surgery. Glaucoma filtration surgery can be defined as an attempt to lower intraocular pressure (IOP) by the surgical formation of an artificial drainage pathway from the anterior chamber to the subconjunctival space. Many types of glaucoma filtration surgery have been developed since the first attempts almost 180 years ago. The wide range of new techniques and devices currently under investigation is testament to the limitations of current techniques and the need for improved therapeutic outcomes. Whilst great attention has been paid to surgical techniques and devices to create the drainage pathway, relatively little attention has been given to address the question of why drainage from such artificial pathways is often problematic. This is in contrast to normal drainage pathways which last a lifetime. Furthermore, the consequences of potential changes in aqueous humour properties induced by glaucoma filtration surgery have not been sufficiently addressed. The mechanisms by which aqueous fluid is drained from the subconjunctival space after filtration surgery have also received relatively little attention. We propose that factors such as the degree of tissue damage during surgery, the surrounding tissue reaction to any surgical implant, and the degree of disruption of normal aqueous properties, are all factors which influence the successful formation of long term drainage channels from the conjunctiva, and that these channels are the key to successful filtration surgery. In recent years it has been suggested that the rate of fluid drainage from the subconjunctival space is actually the determining factor in the resultant IOP reduction. Improved knowledge of aqueous humour induced changes in such drainage pathways has the potential to significantly improve the surgical management of glaucoma. We describe for the first time a novel type of drainage surgery which attempts to minimise surgical trauma to the overlying conjunctiva. The rationale is that a healthy conjunctiva allows drainage channels to form and less opportunity for inflammation and scar tissue formation which are a frequent cause of failure in glaucoma filtration surgery. Successful drainage over extended periods of time has been demonstrated in monkey and rabbit eyes. Long lasting drainage pathways were clearly associated with the presence of lymphatic drainage pathways. A new philosophy in glaucoma drainage surgery is proposed in which minimisation of surgical trauma to the conjunctiva and the encouragement of the development of conjunctival drainage pathways, particularly lymphatic pathways, are central pillars to a successful outcome in glaucoma filtration surgery.

Glaucoma management trends in Australia and New Zealand

BACKGROUND

To describe self-reported patterns of care for glaucoma of ophthalmologists in Australia and New Zealand and summarize current practice styles and patterns associated with glaucoma management.

METHODS

A questionnaire of glaucoma management practices was mailed to all ophthalmologists registered with the Royal Australian and New Zealand College of Ophthalmologists in June 2003. The questionnaire assessed practice preferences for medical management, examination techniques and indications for surgery. The results were cross-tabulated by age, country and subspecialty training in glaucoma.

RESULTS

Fifty-one per cent of 761 surveys were returned, 14% being from glaucoma specialists. New Zealand ophthalmologists proceeded to surgical management of glaucoma earlier than did their Australian colleagues. Australian ophthalmologists tended to use argon laser trabeculoplasty more frequently. Ninety-six per cent of ophthalmologists routinely use gonioscopy in diagnosing glaucoma. Disc drawings and recording cup:disc ratios were the most commonly used methods of documenting disc morphology; glaucoma specialists were more likely to use imaging technologies. SITA-Standard 24-2 was the most commonly used modality of perimetry, and was favoured by glaucoma specialists.

CONCLUSIONS

This survey represents the first Australian and New Zealand effort to identify glaucoma management practices. Although a substantial consensus was found in most areas of treatment, a few areas showed diversity. The information gathered will enable ophthalmologists to compare their own practices with those of their colleagues. In addition, this survey provides a baseline allowing future trends in management to be determined.

Efficacy of glaucoma filtration surgery in pseudophakic patients with or without conjunctival scarring

PURPOSE

To analyze the intraocular pressure (IOP), glaucoma medication requirements, and visual acuity after glaucoma filtration surgery in pseudophakic eyes.

SETTING

Private practice, Boston, Massachusetts, USA.

METHODS

The results of glaucoma filtration surgery in 47 eyes of 40 pseudophakic patients with a minimum follow-up of 1 year were retrospectively reviewed. Eyes with previously surgically manipulated conjunctiva in the area of filtration were compared to eyes without previous manipulation.

RESULTS

Preoperatively, the mean IOP was 25 mm Hg +/- 7.3 (SD); mean number of glaucoma medications, 3.3 +/- 1.0; and mean logMAR visual acuity, 0.41 +/- 0.38. At the final follow-up visit (mean 36.5 +/- 31.5 months), the respective means were 13.6 +/- 6.6 mm Hg (P<.001), 0.9 +/- 1.4 (P<.001), and 0.46 +/- 0.43 (P=.53). The mean postoperative IOP, glaucoma medication requirements, and visual acuity at the final follow-up in eyes with virgin conjunctiva and eyes with previously manipulated conjunctiva were, respectively, as follows: IOP, 12.5 +/- 3.2 mm Hg and 14.1 +/- 7.6 mm Hg (P=.52); medications, 1.1 +/- 1.3 and 0.9 +/- 1.4 (P=.66); and logMAR acuity, 0.6 +/- 0.52 and 0.4 +/- 0.39 (P=.23).

CONCLUSIONS

Glaucoma filtration surgery in pseudophakic eyes significantly improved IOP and reduced glaucoma medication requirements while maintaining stability of vision. There were no statistically significant differences in final IOP, glaucoma medication requirements, or visual acuity between eyes with virgin conjunctiva and eyes with previously surgically manipulated conjunctiva.

Results of phacoemulsification in eyes with preexisting glaucoma filters

PURPOSE

To evaluate the intraocular pressure (IOP), best corrected visual acuity (BCVA), and glaucoma medication requirements in patients having phacoemulsification after preexisting glaucoma filters.

SETTING

Ophthalmic Consultants of Boston, Boston, Massachusetts, USA.

METHODS

A retrospective analysis of 58 eyes that had temporal phacoemulsification via a clear corneal (32 eyes) or a scleral tunnel (26 eyes) approach after filtration surgery was performed with a minimum follow-up of 12 months. Two-tailed homoscedastic t tests were used for statistical analysis.

RESULTS

The mean preoperative IOP in all eyes was 11.8 mm Hg +/- 4.2 (SD), and the mean final postoperative IOP was 13.7 +/- 4.6 mm Hg (P<.022). The mean preoperative logMAR equivalent BCVA was 0.8 +/- 0.4, which improved to a mean of 0.4 +/- 0.4 postoperatively (P<.0000002). There was no statistically significant change in glaucoma medication requirements postoperatively. The differences in IOP, BCVA, and postoperative glaucoma medication requirements were not statistically significant between the clear corneal group and the scleral tunnel group or between patients who received mitomycin at the time of filtration surgery and those who did not. There were no intraoperative complications; 1 patient required additional glaucoma surgery.

CONCLUSION

Clear corneal or scleral tunnel phacoemulsification in the setting of a preexisting glaucoma filter was associated with improved BCVA, a small but statistically significant increase in IOP, and stability in the number of glaucoma medicines required for IOP control over a minimum follow-up of 1 year.

Primate retina imaging with polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PSOCT) is applied to determine the depth-resolved polarization state of light backreflected from the eye. The birefringence of the retinal nerve fiber layer (RNFL) was observed and measured from PSOCT images recorded postmortem in a Rhesus monkey. An image-processing algorithm was developed to identify birefringent regions in acquired PSOCT retinal images and automatically determine the thickness of the RNFL. Values of the RNFL thickness determined from histology and PSOCT were compared. PSOCT may provide a new method to determine RNFL thickness and birefringence for glaucoma diagnostics.

Glaucoma surgery treatment patterns of ASCRS members--2000 survey

A survey of glaucoma surgery parameters was mailed to all the United States members of the American Society of Cataract and Refractive Surgery in 1999 and 2000. Of the 5659 surveys mailed, 725 (13%) were returned. The survey assessed parameters used in glaucoma surgical treatment. Preferred surgery treatment patterns were cross-tabulated with fellowship training in glaucoma (9.3%) and geographic location. This report summarizes current practice styles and patterns of comprehensive ophthalmologists in the United States as derived from the survey.

The use of the G1 and Octosmart programs in detecting temporal changes in the visual field

PURPOSE

The Octopus program Octosmart is able to classify visual fields into six classes. In the program a horizontal bar indicates these classes, and an indicator points to the most probable position, related to the measured pathology. The width of this dashed indicator shows the range of possible fluctuations in the measurement and, therefore, its precision. This study sets out to analyse the suitability of this display mode using other visual-field index data.

METHODS

The visual fields of 83 glaucomatous eyes of 61 patients of various etiological groups and glaucoma suspects were studied for periods varying from 1 to 5 years in a retrospective study. All examinations were performed with the G1 Octopus program and analyzed with the Octosmart program. The statistical significance of linear trends of the visual-field indices, mean defect (MD) and corrected loss variance (CLV), and the class shown by the indicator (POI = position of indicator) were determined, and their regression coefficients were analyzed by means of a linear trend test as a function of time.

RESULTS

Of the sample of 83 tested eyes, a total of 18 significant trends were recorded after five examinations. All visual-field indices showed a trend towards amelioration.

CONCLUSIONS

The 18 significant trends observed must be attributed to perturbing long-term fluctuations and, despite their statistical significance, are of little clinical value. It is questionable whether an increased number of examinations per eye would have attenuated the threshold fluctuations sufficiently to make the change in field class more reliable.

The multifocal ERG in open angle glaucoma--a comparison of high and low contrast recordings in high- and low-tension open angle glaucoma

High and low contrast multifocal ERG (MF-ERG) recordings were obtained from the right eyes of 24 patients with OAG (high-tension OAG: n=16, low-tension OAG: n=8) and compaired to those recorded from 18 healthy volunteers. High contrast MF-ERG recordings were obtained at a mean luminance of 100 cd/m2 with a contrast of 99%, while low contrast MF-ERGs were obtained at a mean luminance of 100 cd/m2 with a contrast of 50%. During MF-ERG recordings the central 50 degrees of the retina were stimulated by 103 hexagons. A MF-ERG recording lasted eight minutes, a M-sequence of 2(15) was used. The first order response component (KI, mean focal flash response) and the first and second slice of the second order response component (mean focal two flash interaction of flashes one, KII. 1, or two, KII.2, base intervals apart) were analyzed for group differences. Group differences were found mainly in latency measures. These included a delay in the central response average of the first positive peak, P1, in KII.2 (p < or = 0.05) in OAG high contrast recordings. Low contrast recordings showed a significant delay in the central response average of the first negative peak, Nl, in KII.2 as well as in the peripheral response average of N1 in KI and of P1 in KII.2 (p<0.05) in OAG. Amplitudes were only affected significantly in KI of the low contrast recordings. Here the amplitude N1P1 was significantly higher in high tension (n=16) than in low tension (n=8) OAG patients. However, an overlap in all of the response parameters tested allowed only group differences to be characterized. Under these stimulus conditions, neither high contrast recordings nor low contrast recordings seem sensitive enough to reliably recognize early glaucomatous retinal dysfunction.

Impact of intraocular pressure regulation on visual fields in open-angle glaucoma

OBJECTIVE

To investigate the correlation of different parameters of intraocular pressure (IOP) to visual field decay in open-angle glaucoma.

DESIGN

Analysis of visual field decay during a prospective, randomized clinical trial comparing primary laser trabeculoplasty with medication.

PARTICIPANTS

Of a total of 82 included eyes in 82 patients with newly detected high-pressure open-angle glaucomas, 76 (55 capsular, 21 simple) fulfilled the 2-year follow-up with the stated number of reliable visual field examinations and were included in this analysis.

INTERVENTION

Automated perimetry and a daytime IOP curve were taken every second month during the 2-year follow-up.

MAIN OUTCOME MEASURES

Six IOP parameters were evaluated and correlated to visual field outcome. The subgroups with the two types of glaucoma (capsular and simple) were analyzed separately.

RESULTS

Visual field decay showed greater correlation to IOP variation (range and peak) and mean IOP than IOP at start or degree of IOP reduction. The relation between mean IOP and visual field decay in the whole group was not quite linear, with more decay at higher IOP levels. The association between IOP regulation and visual field decay was most pronounced in capsular glaucoma, whereas the results in the small group of simple glaucomas were inconclusive.

CONCLUSIONS

Visual field prognosis in high-pressure open-angle glaucoma, essentially capsular glaucoma, is better in patients with smaller IOP variation and poorer in patients with high mean IOP.

The risk profile of glaucoma filtration surgery

Glaucoma surgery has evolved over the past 30 years from the full-thickness procedure to the guarded filtration procedure. However, many of the risks and complications attendant with the full-thickness procedure, including endophthalmitis, hypotony, cataract progression, and filtration failure, continue to plague the glaucoma surgeon performing the guarded filtration procedure, although at lower incidences. With proper modification of technique, such as with postoperative bleb titration and use of adjunctive antifibrotic therapy based on prognosticators for failure, the success rates of trabeculectomy reoperations can approach those of primary trabeculectomy. Such risk factors for failure include African-American race, higher preoperative intraocular pressures, previously failed filters, younger age, and uveitic and neovascular glaucomas. In this paper, we review a number of studies that analyze the risks, complications, and long-term results of glaucoma filtration surgery and discuss different surgical recommendations based on risk factors for failure as well as for performing concomitant cataract and glaucoma surgery.